1. Field of the Invention (Technical Field)
The present invention relates to devices and methods for liquid fuel reverse purge in turbines.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
A typical gas turbine engine includes a fuel atomizer or nozzle for delivery of the fuel to the combustor, where the fuel, in combination with compressed air, is ignited. The resulting combustion gases flow through a turbine that converts combustion energy to mechanical energy capable of driving equipment, such as an electrical generator. The fuel is delivered to the fuel atomizer by means of a fuel pump. When the turbine engine is shut down for any reason, fuel remains in the lines or conduits from the fuel pump through and to the fuel atomizer.
Fuel, particularly liquid fuel, in the lines or conduits, the fuel atomizer, combustor and the like can result in gumming, coking, and similar disadvantageous results. Particularly with the fuel atomizer, this can decrease the operational life of the component thereby resulting in unscheduled removal and replacement or repair. Additionally, cold fuel within the system can interfere with the turbine start-up process, particularly since such fuel is not under pressure, is unmetered and is at a less than optimal temperature for light-off. The fuel remaining in the lines or conduits, the fuel atomizer and the like is essentially lost, and is not effectively used for turbine operation.
U.S. Pat. No. 4,206,595, entitled Fuel Collecting and Recycling System, to Cole, issued Jun. 10, 1980, discloses a recycling fuel system, including a pressure sensitive switch system, including a reservoir within the valve assembly, such that on shutdown fuel is drawn into the valve, and during operation on start-up fuel from the reservoir within the valve assembly is sequenced to the engine.
U.S. Pat. No. 4,539,809, entitled Fuel Pump Vent Drain System, to Stanley and Henry, issued Sep. 10, 1985, discloses a drain line connected to a vent valve, with a check valve and restricted flow orifice. Similarly, U.S. Pat. No. 5,095,694, entitled Fuel Purging System for a Turbine Engine, to Shekleton and Johanson, issued Mar. 17, 1992, discloses a purge system for the fuel injection system of a turbine engine whereby valves connect a purge line to an outlet port, and fuel remaining in the injector is drained into the exhaust conduit. Neither discloses use of the fuel in subsequent operation of the turbine.
U.S. Pat. No. 5,528,897, entitled Fuel Supply System for a Gas Turbine, to Halin, issued Jun. 25, 1996, discloses a fuel supply system for a gas turbine engine that incorporates a discharge conduit which is opened upon an increase in the temperature or pressure of the fuel in the fuel injector. The excess fuel is directed to a receiver or tank. Recovery of the excess fuel is not disclosed.
U.S. Pat. No. 5,701,732, entitled Method and Apparatus for Purging of Gas Turbine Injectors, to Nesbitt and Shoemaker, issued Dec. 30, 1997, discloses a valve and control system whereby, upon interruption of the fuel to the combustor, high pressure air is passed through an air passage to force the fuel in the reverse direction. No pump system is disclosed, and the source of high-pressure air is the compressor of the gas turbine. The system can thus be used when the power demand of the gas turbine shifts from high to low power, such that one or more injectors are shut down.
U.S. Pat. No. 5,927,067, entitled Self Cleaning Augmentor Fuel Manifold, to Hanloser and Harris, issued Jul. 27, 1999, discloses a self-purging gas turbine augmentor or afterburner fuel manifold, operated by core or combustion process gas.
U.S. Pat. No. 5,966,926, entitled Liquid Fuel Injector Purge System, to Shekleton and Martin, issued Oct. 19, 1999, discloses a solenoid valve controlled purge line, which operates together with solenoid valves in the liquid fuel and air assist lines, to purge liquid fuel in the injector and manifold upon shut-down. This utilizes backpressure from the combustor actuated by a solenoid, or alternatively a restrictive orifice.
U.S. Pat. No. 5,809,771, entitled Aircraft Engine Fuel System, to Wernberg, issued Sep. 22, 1998, discloses an xe2x80x9cecology valvexe2x80x9d connected to fuel manifolds, which serves to suction fuel from fuel manifolds upon engine shutdown, temporarily store the fuel in reservoirs in the ecology valve, and return the stored fuel to the manifold upon the next engine operating cycle. In operation, as fuel is supplied on start-up, fuel within the reservoir of the ecology valve is expelled into the fuel line, and thus into the fuel manifolds. However, this does not provide for pre-heating of the fuel.
The invention provides a liquid fuel reverse purge control system for purging a turbine fuel manifold on shutdown of a turbine, which in one embodiment includes (a) a reversible fuel pump for pressurizing fuel from a fuel supply, (b) a fuel manifold in fluidic connection with the reversible fuel pump, (c) at least one solenoid-controlled shutoff valve located in fluidic connection between the reversible fuel pump and the fuel manifold, and (d) an electronic control unit and associated software logic, which electronic control unit is in electronic contact with the reversible fuel pump and the at least one solenoid-controlled shutoff valve, so that on system shutdown the electronic control unit and associated software logic commands the reversible fuel pump to reverse the direction of pumping for a set period of time, and after such set period of time commands the at least one solenoid-controlled shutoff valve to close. In this system, the electronic control unit and associated software logic can command the reversible fuel pump to reverse the direction of pumping within approximately ten seconds of system shutdown, and preferably within approximately one second of system shutdown. The electronic control unit and associated software logic can command the reversible fuel pump to reverse the direction of pumping for a set period of time sufficient to reverse purge all fuel downstream from the reversible fuel pump. In one embodiment, this set period of time is sufficient to reverse purge a volume of fuel equal to at least about 0.8 cubic inches. After the solenoid-controlled shutoff valve is commanded to close, all the fuel has been purged between the solenoid-controlled shutoff valve and the fuel manifold.
The invention also provides a liquid fuel valve manifold for purging a turbine fuel manifold on shutdown of a turbine, the turbine having a fuel pump with an inlet port and an outlet port for pressurizing fuel from a fuel supply and a fuel manifold in fluidic connection with the fuel pump, which liquid fuel valve manifold includes a direct acting solenoid purge valve, having a fuel supply port and a fuel manifold port, wherein on electrical activation the valve connects the fuel support port to the fuel manifold port and on electrical deactivation the value disconnects the fuel support port from the fuel manifold port, and a reverse purge piston slidably disposed within the valve, wherein on electrical deactivation the reverse purge piston suctions fuel from the fuel manifold port. The three-way direct acting solenoid purge valve can further include a re-circulation line port, wherein on electrical deactivation the valve connects the fuel manifold port and the re-circulation line port. In such event, the manifold can also include (a) a two-way direct acting solenoid re-circulation valve, having a purge valve port and a re-circulation line port, wherein on electrical activation the valve is opened and on deactivation the valve is closed, (b) a first re-circulation line in fluidic connection with the purge valve re-circulation line port and the re-circulation valve purge valve port, and (c) a second re-circulation line in fluidic connection with the re-circulation valve re-circulation line port and the inlet port of the fuel pump. The manifold can also include a stored energy mechanism for engaging the reverse purge piston on electrical deactivation, such as a spring or compressed gas. The manifold may also include a cylinder within which the reverse purge piston is slidably disposed. In one embodiment, the reverse purge piston suction fuel volume is equal to at least about 0.8 cubic inches. The manifold may include a first heating mechanism for heating fuel in the second re-circulation line, and a second heating mechanism for heating of fuel remaining within the purge valve. The second heating mechanism may employ heat conduction from the first heating mechanism.
A primary object of the present invention is to provide an apparatus and method to extend turbine operating life, and prevent unscheduled repairs or removals, by reverse purging of the fuel system on shutdown.
Another object of the present invention is to provide an apparatus and method to remove fuel from a turbine fuel atomizer and fuel supply lines thereto on shutdown, thereby limiting coking and increasing component life.
Another object of the present invention is to provide a reverse purge control system under the command of an electronic control unit, thereby integrating reverse fuel purging into operational control of the turbine.
Another object of the present invention is to provide an apparatus and method for reverse fuel purging which employs a mechanical reverse purge mechanism and normally closed, direct acting solenoid valves, such that reverse purging of the fuel system may be effected on any shutdown, including emergency shutdowns wherein there is a loss of electrical power.
Yet another object of the present invention is to provide an apparatus and method for reverse fuel purging in which fuel that is purged is recycled into a re-circulation circuit, such that the fuel may be used during the next turbine operational cycle, and may optionally be heated prior to system start-up under cold conditions.